How does time machine work. I know how the user would use it to go "back in time" and retrieve data but how does the software work? Does it just do compleate copy's or backups of all the data at set times? Also if you end up saving data from a few months.. what happens once the hard drive is full? does it just discard all the old data and replace it with new data?

Do you have to have a compleatly clean formated hard drive to use time machine?

Time Machine only does 1 full backup, the first time it runs. From then on it will only backup files that have changed. When the drive completely fills up, it will start dropping the oldest backup of a file when you have multiple copies. That way you don't actually lose the file, just the oldest revision.

From what I've seen, you do not need a cleanly formatted drive, it just places a single backup file on the drive.

It works so wonderfully, you'll hardly believe it. Easy to use when you want and brainlessly automatic at keeping up. I'm no techie (as my questions and posts demonstrate embarrassingly) but this is the kind of world-beating back-up application that should be built into every OS written for every computer in existence. I think Apple missed a bet by not packaging it separately and charging extra for it -- but very happy to have it included in the Leopard package.

I had done a Carbon Copy Clone of my iMac's HD onto the external drive before installing Leopard. When I started up Time Machine, the application left that previous data alone. It created its own folder of records for its own purposes and that's what it uses.

In addition to what others have already said, Time Machine has already saved me from having to reinstall everything! I had corrupted my system by messing with the resize and merge partition commands in the terminal. So I inserted my Leopard DVD, rebooted and did a full restore from my Time Machine hard drive. It was fast and easy and my system is back to how it was just a few hours ago.

I have a question about it. How much of the system resources does time machine use. Like do you notice or hear it running with less performance in your other apps. Or is it's cpu usage really small so you don't notice it doing it's thing at all?

TM saved me last night. I needed an older version of a document... while working live on a website with 3 other parties on conference, one of them being UPS for integration. WHEW that got dicey. But TM did it's job and the meeting was a success. The site launches Friday evening =)

For my line of work, I only need daily versions, not hourly. So I modified the preference file manually to run every six hours instead of each hour.

The first backup takes a long time, eats up all of your ram, and puts a monopoly on the HD. For the first backup I suggest doing it just before you go to bed. In the morning reboot the machine.

The very awesomest thing about TM is the arrows. Instead of guessing the last time a revision was made to a document... you just select the document and click the 'past' arrow. TM will glide you through time to the very next version of the document. MAGIC.

I've got 78gb worth of stuff on my iMac's HD. Time-Machine set-up took about 80 minutes to handle that initially. Other aps worked more slowly during that time. From what I've seen since, additional back-up intervals have taken seconds.

I generally turn my external HD off and forget it. It comes on again when I turn my machine on in the morning. I let it do its thing for a few seconds and when it's done I turn it off again. Works for me. If I was doing crucial work throughout the course of my day, I'd leave it on.